Apparatus for supplying respiratory gas and a method for controlling the apparatus

ABSTRACT

An apparatus for supplying a respiratory gas includes a conveyor device for conveying the respiratory gas, a conduit for feeding the respiratory gas conveyed by the conveyor device to a person, and a humidification device for humidifying the respiratory gas. A sensor device is configured to generate a signal indicative of the respiratory gas humidity and a control device is configured to control the humidification device with regard to the signal which is generated by the sensor device. A method of supplying a respiratory gas to a patient, in which the respiratory gas is introduced by means of a conveyor device into the conduit leading to the patient and is humidified, includes operating the conveyor device so that a respiratory gas pressure which is above ambient pressure is provided in the conduit, and adjusting the humidity on the basis of signals indicative of the relative and/or absolute humidity of the respiratory gas generated by the sensor device.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 10/487,570, filed Feb. 20, 2004, now U.S. Pat. No. 7,516,740, which is the U.S. national phase of International Application PCT/EP02/09147, filed Aug. 15, 2002 which designated the U.S. and claims priority to German Application No. 101 39 881.6, filed Aug. 20, 2001, the entire contents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention concerns an apparatus for supplying a respiratory gas and a method of controlling the apparatus.

BACKGROUND OF THE INVENTION

In particular for the treatment of sleep-related breathing disorders, it is possible to supply the patient with a respiratory gas, for example filtered ambient air, at a pressure which is increased in relation to the ambient pressure. A respiratory gas pressure which is in the range of between 4 and 18 mbar above the ambient pressure makes it possible to obviate obstructions in the region of the upper respiratory tracts.

It is possible for the pressure of the respiratory gas to be definedly varied. Thus it is possible in particular to control the pressure in such a way that lower respiratory gas pressures obtained during the expiration phases than during the inspiration phases. It is further possible to adapt the respiratory gas pressure in such a way that for example an increased respiratory gas pressure is only set when the person to whom artificial respiration is to be given is in a predetermined stage in sleep. It is further possible for the respiratory gas supplied to the patient to be charged with selected additive substances and, in particular, humidified. Humidification of the respiratory gas can be effected by the gas being brought into contact with warmed water. The degree of humidification of the respiratory gas can be adjusted in that case by way of the temperature of the humidifying water.

SUMMARY OF THE INVENTION

The object of the invention is to provide an apparatus for and a method of supplying a respiratory gas to a breathing person, whereby improved physiological compatibility of the supply of respiratory gas is achieved.

According to the invention that object is attained by an apparatus having the features including a conveyor device for conveying the respiratory gas, a conduit for feeding the respiratory gas conveyed by the conveyor device to a person, a humidification device for humidifying the respiratory gas, a sensor device for generating a signal indicative in respect of the respiratory gas humidity and a control device for controlling the humidification device having regard to the signal which is generated by the sensor device and which is indicative in respect of the respiratory gas humidity.

In that way it is advantageously possible to match the humidity state of the respiratory gas in a narrow tolerance range to the instantaneous physiological demands of the patient. In that way it is advantageously possible to ensure that the respiratory gas is not inadequately or excessively humidified by virtue of an adjustment which is initially implemented on the part of the patient in the context of a deep-sleep phase or upon a change in breathing characteristic.

In accordance with a particularly preferred embodiment of the invention the sensor device for generating a signal indicative in respect of the absolute and/or relative humidity of the respiratory gas is arranged in the region of a breathing mask provided for supplying the respiratory gas.

Alternatively thereto or in a particularly advantageous manner in combination with that feature it is also possible for a sensor device for producing a signal indicative in respect of the humidity state of the respiratory gas to be arranged at the outlet of an air humidification device. By virtue of combined consideration of an air humidity signal generated in the outlet region of an air humidification device and an air humidity signal generated in the region of the patient or mask, it is then possible to check whether an unacceptably great change in the humidity state of the respiratory gas and in particular precipitation of water takes place in the region of a respiratory gas conduit means provided between the breathing mask and the air humidification device.

It is also possible, for example by a temperature detection device provided in the region of the breathing mask, to detect the temperature of the respiratory gas in the region of the patient and, on the basis of an additional humidity signal produced for example in the region of an air humidification device, to assess whether an unacceptably high relative humidity level obtains in the respiratory gas in the region near the patient. Particularly in conjunction with a sensor device provided in the region of the patient for detecting a signal indicative in respect of the humidity state of the respiratory gas, it is advantageously possible to draw a distinction between expiratory humidity states and inspiratory humidity states.

The humidity states ascertained for the respective breathing phases can be taken into consideration in terms of regulating the respiratory gas humidity level, on the basis of a predetermined or preferably adaptively matched regulating procedure.

By virtue of the present invention it is possible to reduce the proportion of water which is entrained in drop form in the respiratory gas. That reliably avoids any germs being transported by way of drops of water.

In accordance with a particularly preferred embodiment of the invention the sensor device is arranged in the region, near a patient, of a respiratory gas conduit system. In that way it is advantageously possible to detect the respiratory gas humidity state which is actually relevant to the user. In that respect, in a particularly advantageous configuration, the sensor device is arranged in the region of a breathing mask and in particular is integrated into the breathing mask. In that respect the sensor device is preferably of such a design configuration that the measurement dynamics thereof are considerably higher than the breathing rate of the patient. In that way it is possible to specifically detect the humidity state of the respiratory gas for the respective breathing phases. The measurement values which are detected in that way for the expiration phase and for the inspiration phase, in regard to respiratory gas humidity level, can be evaluated by a preferably adaptively optimized regulating procedure. It is possible to disregard the respiratory gas humidity values ascertained in respect of the expiration phase or to take them into account only as control values, and to implement adjustment of the respiratory gas humidity essentially having regard to the respiratory gas humidity values detected in respect of the inspiration processes.

As an alternative to arranging the sensor device in the region near the patient—or in a particularly advantageous fashion in combination therewith—it is possible for the sensor device or a further sensor device to be arranged in the region between the breathing mask and a hose conduit portion, and in particular to integrate it into a coupling structure or a washing-out valve arrangement.

The sensor device can also be arranged in the region of the humidification device so that the humidity state of the respiratory gas can be directly detected by way of the sensor device and the operating performance of the humidification device can be matched in regard to a desired respiratory gas reference humidity state, having regard to the instantaneous respiratory gas humidity level.

In accordance with a particularly preferred embodiment of the invention the sensor device includes an electrical sensor element, wherein provided in the region of that sensor element is an electronic circuit, for the generation of a data sequence, by way of which the respiratory gas humidity measurement signals detected on the part of the sensor element can be transmitted in encoded form. Processing of the respiratory gas humidity signals detected by the sensor element in the region of the sensor element itself makes it possible substantially to avoid falsification of the signal, for example because of the transmission properties of any signal lines.

The sensor element is preferably designed in such a way that it detects the respiratory gas humidity on the basis of inductive, capacitive and/or thermal interaction effects. As an alternative thereto or also in combination with the use of physical measurement principles of that kind, it is also possible to detect the respiratory gas humidity by optical means.

In accordance with a particularly preferred embodiment of the invention a signal indicative in respect of the temperature of the respiratory gas is also generated on the part of the sensor device. Insofar as that is not the case, it is possible for a measuring device which is suitable for detecting the temperature of the respiratory gas to be preferably also arranged in the immediate proximity of the sensor element.

It is possible for the sensor device for detecting the respiratory gas humidity to be arranged in the region of the humidification device and for a temperature detection device to be provided in the region near the patient. On the basis of the respiratory gas humidity state detected in the region of the humidification device and the respiratory gas temperature detected in the region of the patient, it is possible to detect the relative humidity level of the respiratory gas at the patient. The measurement values detected on the part of the temperature detection device or also the humidity sensor device can also be taken into consideration in actuation of the conveyor device, besides actuation of the humidification device. Thus, on the basis of the measurement values generated by the humidity sensor device and/or the temperature detection device, it is possible to implement a breathing phase recognition operation and to modulate the respiratory gas pressure in accordance with the recognized breathing phases.

The operation of ascertaining a reference respiratory gas humidity value which is relevant for operation of the humidification device is preferably effected having regard to a data set, in particular an adaptively optimized data field, which takes account of the sleep state of the patient, the breath volume of the patient and for example also the position of sleep of the patient, and in particular the degree of neck rotation thereof. Thus it is possible for example, in periods of time in which the patient is sleeping on one side, to actuate lower respiratory gas humidity levels than for example in a situation involving a supply of respiratory gas when lying on the back.

Adjustment of the humidification output of the humidification device, such adjustment being effected in accordance with the signals generated by the humidity sensor device, is effected preferably by altering the temperature of the humidification water which comes into contact with the respiratory gas.

As an alternative to or also in combination with the above-described measure it is also possible to alter the humidification output of the humidification device for example by altering the effective water surface area available for humidification purposes. It is also possible for the respiratory gas temperature and in particular the temperature of the respiratory gas to be definedly adjusted before it comes into contact with the humidification water.

It is also possible to alter the flow characteristic of the air coming into contact with the humidification water, in such a way that the respectively desired respiratory gas humidity values checked by the sensor device occur at the outlet of the humidification device.

An embodiment of the invention, which is advantageous in regard to particularly precise conditioning of the respiratory gas in respect of the moisture contained therein is afforded if, if necessary, only a partial flow of the respiratory gas is brought into contact with the humidification water, wherein the respiratory gas humidity level is determined by way of the ratio of the partial flow of respiratory gas which has come into contact with the humidification water, and the partial flow of respiratory gas which is taken past the humidification device. It is possible for the conduit means to be passed through the humidification device in such a way that a respiratory gas which is pushed back over the humidification device during an expiration phase does not come into contact with the humidification water.

An embodiment of the invention, which is advantageous in regard to a particularly high level of handling comfort, is provided in that, disposed in the region of the sensor device for detecting the respiratory gas humidity is a transmitting device for wireless transmission of the data sequence generated in respect of the respiratory gas humidity. A transmitting device of that kind can be for example in the form of a blue tooth transmitting device. It is also possible for the signals generated on the part of the sensor device to be transmitted back to the humidification device optically, in particular in the form of infrared signals. When using a respiratory gas conduit produced from a material which is transparent at least in the infrared range, it is possible for the respiratory gas hose conduit to be used as an optical waveguide, by way of which the signals generated on the part of the sensor device can be transmitted to the humidification device or to a control device provided for controlling the humidification device.

The object of the invention as specified in the opening part of this specification is further attained in accordance with the invention by a method of supplying a respiratory gas to a patient, in which the respiratory gas is introduced by means of a conveyor device into a conduit system leading to a patient and is humidified, wherein the conveyor device is operated in such a way that a respiratory gas pressure which is above ambient pressure at least in phase-wise manner obtains in the air conduit system, wherein signals indicative in respect of the relative and/or absolute humidity of the respiratory gas are generated by means of a sensor device and the humidity of the respiratory gas is adjusted on the basis of the signals generated in that way.

In accordance with a particularly preferred embodiment of this method the humidity of the respiratory gas is detected in the region near the patient, in particular in the region of a breathing mask. In that way it is in particular possible to detect the respiratory gas humidity level both for the expiration phases and also for the inspiration phases and to take account of the measurement values individually obtained in that way, in ascertaining a reference respiratory gas humidity value.

The method according to the invention and also the above-described apparatus are particularly advantageously suitable for the artificial respiratory and breathing therapy sector. Humidification of the respiratory gas can also be effected in particular by ultrasonic atomizers, bubble vaporizers, surface contact humidifiers and injection systems. The dynamics of the respiratory gas humidification operation is preferably selected to be so high that in particular unacceptably high or also unacceptably low respiratory gas humidity values can be sufficiently quickly adjusted.

In regard to regulation of the respiratory gas temperature and/or the respiratory gas humidity content, preferably the following control parameters (X) are evaluated: the respiratory gas volume flow, the respiratory gas temperature, the humidity content of the respiratory gas in terms of relative and/or absolute humidity, levels of gas concentration, in particular CO₂ saturation, the therapy pressure and/or the mask pressure and/or the difference between a therapy reference pressure and the mask pressure actually occurring at the patient, polysomnographic parameters such as snoring, heart rate, oxygen saturation, body position; and ambient conditions such as air pressure, temperature and humidity and preferably also EEG-signals, in particular measurement values which are derived therefrom and are indicative in respect of the sleep phase.

The respiratory gas temperature and/or the respiratory gas humidity can be adjusted by way of the water surface area (preferably by varying the effective water surface area in the air humidifier) and/or the amount of water (preferably by means of the amount of water in the air humidifier) and/or the water temperature (preferably by heating or cooling the water and/or water molecules in the air) and/or the respiratory gas temperature (preferably by heating or cooling the respiratory air) and/or the mixing of gases (preferably by mixing various gases, for example dry air with mist of high humidity or also by mixing gas flows involving differing temperatures and/or air humidity levels and also by variable flow resistances in the region of the air humidifier.

Further details of the invention will be apparent from the description hereinafter with reference to the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagrammatic view to illustrate the structure of an apparatus according to the invention, and

FIG. 2 shows a regulating circuit according to the invention for adjusting the respiratory gas humidity level.

DETAILED DESCRIPTION OF THE INVENTION

The system shown in FIG. 1 for supplying a respiratory gas includes a respiratory gas conveyor device 1, a respiratory gas humidification device 2 coupled thereto, and a breathing mask device 4 coupled to the respiratory gas humidification device 2 by way of a flexible hose conduit 3 a.

The respiratory gas humidification device 2 can also be coupled in the form of what is known as a stand-alone unit to the respiratory gas conveyor device 1 by way of a preferably flexible hose conduit 3 b. As an alternative thereto it is also possible for the respiratory gas humidification device 2 and the respiratory gas conveyor device 1 to be combined together to form an integral unit.

Disposed in the region of the conduit system which is provided to convey the respiratory gas and which is formed by the respiratory gas conveyor device 1, optionally the flexible hose conduit 3 b, the respiratory gas humidification device 2, the flexible hose conduit 3 a and in particular also the breathing mask device 4, there is at least one sensor device for detecting the humidity state of the respiratory gas being conveyed. In the embodiment illustrated here, provided in particular in the region of the breathing mask device 4 is a humidity sensor 5, by way of which a signal indicative in respect of the respiratory gas humidity state is generated and passed to a control device CPU. The control device CPU can either be arranged in the region of the humidity sensor 5 or can preferably be integrated into the respiratory gas humidification device or the respiratory gas conveyor device 1.

The respiratory gas humidification device 2 can be actuated on the basis of the signals generated on the part of the humidity sensor 5, in such a way that the humidity state of the respiratory gas which is humidified in the respiratory gas humidification device 2 takes account, in a close tolerance range, of the instantaneous physiological needs of the person being afforded respiration by way of the breathing mask device 4.

In determining the reference respiratory gas humidity state which is decisive at the present time, besides the signals generated by the humidity sensor 5, the procedure preferably also takes account of a performance graph or array which for example takes account of further polysomnographic parameters such as for example the degree of oxygen saturation of the blood of the person to whom respiration is being administered, noises, in particular snoring events as well as the heart rate and the instantaneous breathing characteristic. It is also possible, when calculating the reference humidity state of the respiratory gas, to take account of stages in sleep, ambient conditions as well as other physiological parameters, in particular the position in which the patient sleeps.

The system illustrated here has further sensor devices 5 a, 5 b by which signals are generated, used for defined conditioning of the respiratory gas. The sensor device 5 b involves a sensor device for generating signals indicative in respect of the respiratory gas temperature: by taking account of the respiratory gas temperature signal generated on the part of the sensor device 5 b, it is possible definedly to adapt the humidification output of the humidification device, as is required to achieve a desired reference humidity state.

It is possible by means of the sensor 5 a provided in the region of the humidification device 2 to detect the humidity state of the respiratory gas immediately after it has been charged with water.

By taking account of the signal generated by the sensor device 5 a disposed in the ambient region of the respiratory gas humidification device and also the signal generated by the sensor device 5 in the region near the mask, it is then possible to recognize any changes in state of the respiratory gas, caused by the flexible hose conduit 3 a, in particular the formation of condensation water in the flexible hose conduit 3 a, and on the basis thereof to implement corrections to the humidification output of the respiratory gas humidification device 2.

The sensor device 5 provided in the region of the breathing mask device 4 preferably includes a sensor element for detecting the humidity state on the basis of electromagnetic interactions, in particular capacitive interactions. The measurement signals generated by the sensor element are preferably converted into a digital data format by a connected measurement circuit while still in the region of the sensor element, and transmitted to the CPU by way of a preferably potential-free measurement data output.

It is possible for transmission of the humidity signals generated in the region of the breathing mask to be implemented by way of a data line which is preferably integrated into the flexible hose conduit 3 a or is at least guided along same.

As an alternative thereto it is also possible for the measurement signals generated on the part of the humidity sensor 5 to be transmitted wirelessly, for example by way of a blue tooth arrangement, to the CPU or also to other detection devices. In this case the voltage supply for the humidity sensor 5 is preferably effected by means of a voltage source provided in the region of the breathing mask device 4, for example in the form of a button cell or a solar cell.

The respiratory gas humidification device 2 may include for example an ultrasonic atomizing device, a bubble vaporizer or a surface contact humidifier. Preferably the humidification output of the humidification device 2 can be matched to the required humidification output within a time window which does not exceed a duration of 10 minutes.

FIG. 2 diagrammatically shows a preferred embodiment of a regulating circuit for controlling the humidity state of the respiratory gas. That regulating circuit makes it possible to individually match the respiratory gas temperature and/or the respiratory gas air humidity to the instantaneous physiological state of the patient, that is to say to increase it or reduce it in phase-wise manner.

Preferably the following control parameters (X) are evaluated for the purposes of regulating the respiratory gas state:

-   -   volume flow;     -   respiratory gas temperature;     -   humidity content of the respiratory air in terms of relative         and/or absolute humidity;     -   levels of gas concentration (gas composition, in particular O₂         content);     -   therapy pressure and/or mask pressure and/or delta between         therapy pressure and the actually applied mask pressure;     -   polysomnographic parameters such as snoring, heart rate, oxygen         saturation, body position;     -   ambient conditions such as air pressure, temperature and         humidity content;     -   EEG (sleep phase such as NREM 1-4, REM);     -   mathematical control values (X_(M));     -   mathematical calculations from the control parameters.

Preferably the following initial parameters (Y) are regulated for the respiratory gas temperature and/or respiratory gas humidity:

-   -   water surface area (preferably by altering the effective water         surface area in the air humidifier); and/or     -   amount of water (preferably by way of the amount of water which         is in the air humidifier); and/or     -   water temperature (preferably by heating or cooling the water         and/or water molecules in the air); and/or     -   respiratory gas temperature (preferably by heating or cooling         the respiratory air); and/or     -   mixing gases (preferably by mixing various gases, for example         dry air with mist/of high humidity at differing temperatures         and/or with differing air humidity); and/or     -   flow resistances (preferably by way of the flow speed in the         system).

The evaluation operation is preferably effected on the basis of the evaluation algorithm described hereinafter:

1st Feature

At least one control parameter (X) or a suitable combination is required for regulating the respiratory temperature and/or the respiratory humidity.

2nd Feature

The control parameters are evaluated over a given time interval, preferably over the expiration and inspiration time. The measurement values obtained in that way, within an interval, are subjected to further mathematical calculation, preferably maxima and/or minima and/or delta between minimum and maximum and/or mean values.

3rd Feature

Typical behavior patterns on the part of the patients can be calculated from the control parameters (X). Thus, it is possible to establish the instantaneous breathing state by virtue of the reverse correlation of given control parameters (X), for example volume flow, temperature fluctuation in the respiration air, that is to say it is possible to draw a distinction between stable respiration (uniform amplitudes and regular respiration rate) and unstable respiration (irregular amplitude and respiration rate, periodic respiration) and regulation can be implemented on the basis of the mathematical control values (X_(M)).

The mode of operation of a respiratory gas supply system according to the invention is described hereinafter.

Control Parameters:

Volume Flow:

1. If the measured volume flow exceeds a limit value (for example due to mouth leakage), an increase in the respiratory gas temperature or an increase in respiration humidity is preferably effected. If the measured volume flow falls below a limit value (for example due to a low breath volume), cooling of the respiratory gas temperature or a reduction in respiration humidity is preferably effected.

2. A distinction can be made between stable respiration (uniform amplitude and regular respiration rate) and unstable respiration (irregular amplitude and respiration rate, periodic respiration) preferably by reverse correlation from the volume flow. The respiratory gas temperature and the respiration humidity is regulated by the result of the reverse correlation.

Respiratory Gas Temperature:

1. If the measured respiratory gas temperature falls below a limit value (for example due to mouth leakage), an increase in the respiratory gas temperature or an increase in respiratory gas humidity is preferably effected. If the measured respiratory gas temperature exceeds a limit value (for example due to a low breath volume), cooling of the respiratory gas temperature or a reduction in respiration humidity is preferably effected.

2. Both the temperature fluctuations during inspiration and expiration can be evaluated. The temperature difference measured from breathing in and breathing out is used as a regulating parameter. In the case of big breaths (large volume flow) the temperature delta between inspiration and expiration is highly pronounced so that preferably the respiratory gas temperature or respiration humidity is increased.

3. A distinction can be made between stable respiration (uniform amplitude and regular respiration rate) and unstable respiration (irregular amplitude and respiration rate, periodic respiration) preferably by reverse correlation from the respiratory gas temperature. The respiratory gas temperature and the respiration gas humidity are regulated by the result of the reverse correlation.

Humidity:

The respiratory air humidity is measured during expiration and inspiration. Humidity measurement can be effected both relatively and also absolutely.

1. The expiration and inspiration measurement values obtained in that way are further mathematically calculated, preferably over a time interval in which the minimum and/or the maximum and/or the delta between minimum and maximum and/or the mean value is formed.

2. The control parameter humidity can also be combined for example in dependence with the ambient temperature, kind of respiration (reverse correlation).

Initial Parameters:

Gas Concentration:

1. The respiratory gas humidity and/or the respiratory gas temperature can be regulated by mixing dry and humid air. Thus it is possible to branch off the air flow so that the air is passed over the surface of the water and/or over the cooling/heating means.

Flow Resistance:

1. The flow resistance within the air humidifier can be altered. If for example a high level of air humidity is required then contact or the residence time in the humidifier can be increased by increasing the flow resistance in the air humidifier.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A method of determining humidity of gas delivered to a patient, the method comprising: evaluating a relative humidity level and a temperature of ambient air outside a patient circuit that delivers a flow of gas to an airway of the patient, wherein the patient circuit comprises a humidifier chamber configured to contain a supply of water; conveying ambient air into the patient circuit; humidifying the ambient air conveyed into the patient circuit by conveying the ambient air over a surface of the supply of water; and regulating a relative humidity level and a temperature of the humidified air based on (a) the relative humidity level and the temperature of the ambient air outside the patient circuit, and (b) a rate at which the ambient air that is conveyed into the patient circuit is humidified.
 2. A method according to claim 1, further comprising: regulating the rate based on a temperature of the supply of water within the humidifier chamber, a volume flow of the ambient air conveyed in the patient circuit, or a combination thereof.
 3. A method according to claim 1, further comprising: evaluating the rate based on at least one parameter, the at least one parameter selected from a group comprising a volume flow of air in the patient circuit, the temperature of the humidified air, the humidity of the humidified air, a level of gas concentration of the humidified air, a pressure of the humidified air, at least one polysomnographic parameter, a pressure of the ambient air, the temperature of the ambient air, and an EEG measurement.
 4. A method according to claim 3, wherein evaluating the rate based on the level of gas concentration of the humidified air comprises evaluating an O₂ content of the humidified air.
 5. A method according to claim 3, wherein the at least one polysomnographic parameter comprises at least one of snoring, heart rate, oxygen saturation, and/or body position.
 6. A method according to claim 3, wherein the at least one parameter is evaluated over a time interval, and evaluating the rate comprises determining a maximum value of the at least one parameter, a minimum value of the at least one parameter, a delta between the maximum value and the minimum value, and/or a mean value of the at least one parameter.
 7. A method according to claim 1, further comprising: regulating the rate by regulating a surface area of the supply of water in the humidifier chamber, an amount of water in the humidifier chamber, a temperature of the water in the humidifier chamber, the temperature of the humidified air, and/or a flow resistance and/or by mixing air of different temperatures and/or humidities, or any combination of regulating and mixing thereof.
 8. A method according to claim 7, wherein regulating the flow resistance comprises regulating a flow speed.
 9. A method of determining humidity of gas within a patient circuit, the method comprising: evaluating a relative humidity level and a temperature of ambient gas outside the patient circuit, wherein the patient circuit comprises a humidifier chamber configured to contain a supply of water; conveying ambient gas into the patient circuit by conveying the ambient gas over a surface of the supply of water; increasing a pressure and the humidity of the ambient gas drawn into the patient circuit; and determining a humidity level of the gas within the patient circuit after the humidity has been added thereto based on (a) the relative humidity level and temperature of the ambient gas outside the patient circuit, and (b) at least one parameter of the gas other than a humidity level within the patient circuit.
 10. A method according to claim 9, wherein the at least one parameter of the gas comprises a volume flow of the gas in the patient circuit and/or a pressure of the gas in the patient circuit.
 11. A method according to claim 9, wherein the humidity level of the gas is also determined based on (c) a rate at which humidity is added to the gas.
 12. A method according to claim 11, wherein the rate is estimated based at least on a temperature of the supply of water within the humidifier chamber.
 13. A method of delivering gas to a patient along a patient circuit, wherein a pressure of the gas within the patient circuit is elevated by a gas conveyor device, and the humidity level of the gas within the patient circuit is elevated by a humidifier, the method comprising: determining the humidity of the gas within the patient circuit according to the method of claim 9; evaluating the pressure of the gas within the patient circuit; evaluating a volume flow of the gas within the patient circuit; evaluating at least one parameter of the operation of the humidifier; and regulating a humidity level of the gas in the patient circuit downstream from the humidifier based at least in part on the volume flow of the gas within the patient circuit, the pressure of the gas within the patient circuit, at least one parameter of the ambient gas outside the patient circuit comprising (a) the relative humidity level, (b) the temperature, (c) an absolute humidity level, (d) a pressure, or (e) any combination thereof, and the at least one parameter of the operation of the humidifier.
 14. A method according to claim 13, wherein the at least one parameter of the operation of the humidifier comprises a temperature of water in the humidifier.
 15. A method according to claim 13, wherein the at least one parameter of the operation of the humidifier comprises a surface area of water in the humidifier, an amount of water in the humidifier, a temperature of the humidified gas, a flow resistance, or any combination thereof.
 16. A method according to claim 13, further comprising: determining a humidity level to which the humidity level of the gas within the patient circuit can be elevated without forming condensation within the patient circuit based on (a) the flow rate of the gas within the patient circuit, (b) the pressure of the gas within the patient circuit, (c) the at least one parameter of the operation of the humidifier, (c) the at least one parameter of the ambient gas outside the patient circuit, or (d) any combination thereof.
 17. A method of delivering gas to a patient along a patient circuit, wherein the gas is pressurized by a gas conveyor device within the patient circuit and humidified by a humidifier, the method comprising: determining the humidity of the gas within the patient circuit according to the method of claim 9; evaluating the pressure of the gas within the patient circuit; evaluating a volume flow of the gas within the patient circuit; evaluating a temperature associated with the humidifier; and regulating a humidity level of the gas in the patient circuit downstream from the humidifier based at least in part on the volume flow of the gas within the patient circuit, the pressure of the gas within the patient circuit, the relative humidity level and/or an absolute humidity level of the ambient gas outside the patient circuit, and the temperature associated with the humidifier.
 18. A method according to claim 17, wherein the temperature associated with the humidifier comprises a temperature of water in the humidifier, a temperature of the gas humidified by the humidifier, or a combination thereof.
 19. A method of determining humidity of a gas within a patient circuit, the method comprising: conveying ambient air into a patient circuit and through a conduit of the patient circuit to an airway of the patient using a conveyor device; determining a humidity level of the ambient air conveyed into the patient circuit by the conveyor device; humidifying the ambient air conveyed into the patient circuit by passing the ambient air through a humidification chamber of the patient circuit and over a surface of a supply of liquid contained in the humidification chamber, wherein the humidification chamber is provided between the conveyor device and the conduit; determining a rate at which the ambient air is humidified; and determining a humidity level of the humidified air in the patient circuit based on (a) the humidity level of the ambient air, and (b) the rate at which the ambient air is humidified.
 20. A method according to claim 19, wherein the rate at which the ambient air is humidified is determined based on a temperature of the liquid within the humidification chamber, a volume flow of the ambient air in the patient circuit, or a combination thereof.
 21. A method according to claim 19, further comprising: adjusting the rate at which the flow of ambient air is humidified based on the determined humidity level of the humidified air in the patient circuit.
 22. A method according to claim 21, wherein adjusting the rate comprises adjusting a temperature of the liquid in the humidification chamber.
 23. A method according to claim 21, wherein adjusting the rate comprises adjusting a volume flow of the ambient air in the patient circuit.
 24. A method according to claim 21, wherein adjusting the rate comprises adjusting a temperature of the air in the patient circuit.
 25. A method according to claim 24, wherein adjusting the temperature comprises adjusting the temperature of the air prior to the humidification chamber.
 26. A method according to claim 19, wherein adjusting the rate comprises adjusting the rate to provide a desired level of humidity.
 27. A method according to claim 26, wherein the desired level of humidity comprises a maximum humidity to which the humidity can be increased without forming condensation within the conduit.
 28. A method according to claim 19, further comprising adjusting the temperature of the humidified air.
 29. A method of delivering gas to a patient along a patient circuit, wherein the gas is pressurized by a gas conveyor device within the patient circuit and humidified by a humidifier, the method comprising: determining the humidity of the gas within the patient circuit according to the method of claim 19; evaluating a volume flow of the gas within the patient circuit; evaluating a temperature of the ambient air outside the patient circuit; and regulating a humidity level of the gas in the patient circuit downstream from the humidifier based at least in part on the volume flow of the gas within the patient circuit, the humidity level of the ambient air outside the patient circuit, and the temperature of the ambient air outside the patient circuit.
 30. A method according to claim 29, wherein regulating the humidity level comprises regulating the humidity level to a desired humidity level.
 31. A method according to claim 30, wherein the desired humidity level is a desired relative humidity level.
 32. A method according to claim 30, wherein the desired humidity level is a desired absolute humidity level.
 33. A method according to claim 30, wherein the desired humidity level is a maximum humidity level such that condensation will not occur in a conduit of the patient circuit that delivers the gas from the humidifier to the patient.
 34. A method according to claim 29, further comprising: evaluating a temperature associated with the humidifier.
 35. A method according to claim 34, wherein the temperature associated with the humidifier comprises a temperature of water in the humidifier, a temperature of the gas humidified by the humidifier, or a combination thereof.
 36. A method according to claim 35, further comprising: regulating the humidity level of the gas in the patient circuit based in part on the temperature associated with the humidifier.
 37. A method according to claim 29, further comprising: evaluating the pressure of the gas within the patient circuit.
 38. A method according to claim 37, further comprising: regulating the humidity level of the gas in the patient circuit based in part on the pressure of the gas within the patient circuit.
 39. A method according to claim to claim 29, wherein determining the humidity level of the ambient air conveyed into the patient circuit comprises determining a relative humidity and/or an absolute humidity of the ambient air. 